I recently came up with a theory that Sanji might get a power because all his siblings did, even though he was called a dud. I was then watching One Piece Film: Gold and remembered how his flames didn't make any sense. Could his flames have come from his father's experiments?

He did say in Enies Lobby that he got heated up when he was mad and his powers related to fire keep growing a bit stronger than friction should be able to make. His siblings had powers similar to devil fruit users, so the more powerful Sanji's flames become, the less I believe it is natural (by natural I mean through Haki and friction).

still we don't know for sure now but it is possible that it relates to the "modification" that he received and that they have remained dormant. @NamikazeSheena not anymore, after time skip he does not have to spin to ignite his leg
– ProxyFeb 8 '17 at 13:48

It sounds like you are not caught up but he used it under water once too. Another reason I doubt that it is friction but it could be haki. It was either on the fishman island or punck hazard.
– DarthclemFeb 8 '17 at 15:47

@NamikazeSheena For some reason, I seem to remember at least one occasion where sanji did not spin but his foot lit up after the timeskip.
– RyanFeb 8 '17 at 17:12

4 Answers
4

Well, this is an opinion-based question so no clear answer can be given, but I can at least tell my own opinion.

This was a plausible theory for a time, but in my opinion it is now impossible.

Unless I missed something, nothing indicates that Sanji's Diable Jambe comes from anything other than friction. He's been able to activate Diable Jambe without spinning ever since the beginning of the second part of the series, as shown in the manga by his fight against Surume the kraken; long before his family was even mentioned.

He's been stated several times in the Totto Land arc to be a "dud" whose genetic enhancements failed, a statement greatly strengthened by a revelation from chapter 852.

Sanji's mother Sora is the reason why his enhancements failed. When she was forced by her husband to subject herself to experiments to allow her then-unborn sons to be genetically altered, she took a drug potent enough to counteract those alterations, in an attempt to cancel them. While this didn't work with Sanji's brothers, it did work with Sanji himself, who turned out as normal and full of empathy and compassion as any normal human.

The above moment's entire meaning and point would be completely shattered if Sanji suddenly turned out to have altered genes after all, hence why I think the theory is impossible. However, this is only my opinion of course, as no clear answer can be given yet.

When Luffy meets him on Wholecake Island, Sanji fights him. His kicks were crushing all the databases that the the scientists who watched it had. Luffy did not fight back. At the end of the fight, everyone concludes that Sanji is a Vinsmoke afterall. Luffy says he would starve until Sanji brings him food, and stays in his spot. If you read the manga, you will be a bit ahead and know all this.

I am completely caught up and knew most of your spoiler but I don't remember sanji's kicks affecting technology. I just reread the fight between Sanji and luffy but didn't see anything related to technology in the fight.
– DarthclemFeb 9 '17 at 18:10

There were Germa scientists watching. They said " This kick beats all our charts. So he is a Vinsmoke afterall."
– TGamerFeb 9 '17 at 21:03

1

@TGamer your answer is a bit convoluted. Your mixing the battle between Sanji and Luffy with the battle between Sanji and his father.
– CallatFeb 19 '17 at 2:29

Basically, it says that Sanji's abilities were from his genetics and they were activated through his emotions and such. Since he had emotions (which he inherited from his mother) he wasn't able to use his altered genes because he had no real motivation to use them. His brothers and sister on the other hand weren't tied down by emotion so they could use it freely.

When Sanji met Luffy and the others, he had a strong will and conviction to be strong for his nakama and so he used his abilities.

IDK I haven't read the full post in a while so this is the TLDR; you should probably read it. It explains a lot if you think about it.

Multiple characters have been shown to be able to summon fire or explosions by punching or kicking with extreme force. While it is alien in this world that is a reoccurring phenomenon in this world. Those include "Destruction Cannon" Ideo, Luffy, and Kin'emon. Sanji's abilities are unique. They do not necessarily require his family's genetic experiments to fit into the story because of the other similar abilities in canon.

I should point out that he does not burn himself because "while the fire burns hot, his heart burns hotter". This seems mostly a way to toss off the question, but it also sounds like it hints to haki or similar tied to the source of his powers.